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## gMock Cheat Sheet
<!-- GOOGLETEST_CM0019 DO NOT DELETE -->
<!-- GOOGLETEST_CM0033 DO NOT DELETE -->
### Defining a Mock Class
#### Mocking a Normal Class {#MockClass}
Given
```cpp
class Foo {
...
virtual ~Foo();
virtual int GetSize() const = 0;
virtual string Describe(const char* name) = 0;
virtual string Describe(int type) = 0;
virtual bool Process(Bar elem, int count) = 0;
};
```
(note that `~Foo()` **must** be virtual) we can define its mock as
```cpp
#include "gmock/gmock.h"
class MockFoo : public Foo {
...
MOCK_METHOD(int, GetSize, (), (const, override));
MOCK_METHOD(string, Describe, (const char* name), (override));
MOCK_METHOD(string, Describe, (int type), (override));
MOCK_METHOD(bool, Process, (Bar elem, int count), (override));
};
```
To create a "nice" mock, which ignores all uninteresting calls, a "naggy" mock,
which warns on all uninteresting calls, or a "strict" mock, which treats them as
failures:
```cpp
using ::testing::NiceMock;
using ::testing::NaggyMock;
using ::testing::StrictMock;
NiceMock<MockFoo> nice_foo; // The type is a subclass of MockFoo.
NaggyMock<MockFoo> naggy_foo; // The type is a subclass of MockFoo.
StrictMock<MockFoo> strict_foo; // The type is a subclass of MockFoo.
```
**Note:** A mock object is currently naggy by default. We may make it nice by
default in the future.
#### Mocking a Class Template {#MockTemplate}
Class templates can be mocked just like any class.
To mock
```cpp
template <typename Elem>
class StackInterface {
...
virtual ~StackInterface();
virtual int GetSize() const = 0;
virtual void Push(const Elem& x) = 0;
};
```
(note that all member functions that are mocked, including `~StackInterface()`
**must** be virtual).
```cpp
template <typename Elem>
class MockStack : public StackInterface<Elem> {
...
MOCK_METHOD(int, GetSize, (), (const, override));
MOCK_METHOD(void, Push, (const Elem& x), (override));
};
```
#### Specifying Calling Conventions for Mock Functions
If your mock function doesn't use the default calling convention, you can
specify it by adding `Calltype(convention)` to `MOCK_METHOD`'s 4th parameter.
For example,
```cpp
MOCK_METHOD(bool, Foo, (int n), (Calltype(STDMETHODCALLTYPE)));
MOCK_METHOD(int, Bar, (double x, double y),
(const, Calltype(STDMETHODCALLTYPE)));
```
where `STDMETHODCALLTYPE` is defined by `<objbase.h>` on Windows.
### Using Mocks in Tests {#UsingMocks}
The typical work flow is:
1. Import the gMock names you need to use. All gMock symbols are in the
`testing` namespace unless they are macros or otherwise noted.
2. Create the mock objects.
3. Optionally, set the default actions of the mock objects.
4. Set your expectations on the mock objects (How will they be called? What
will they do?).
5. Exercise code that uses the mock objects; if necessary, check the result
using googletest assertions.
6. When a mock object is destructed, gMock automatically verifies that all
expectations on it have been satisfied.
Here's an example:
```cpp
using ::testing::Return; // #1
TEST(BarTest, DoesThis) {
MockFoo foo; // #2
ON_CALL(foo, GetSize()) // #3
.WillByDefault(Return(1));
// ... other default actions ...
EXPECT_CALL(foo, Describe(5)) // #4
.Times(3)
.WillRepeatedly(Return("Category 5"));
// ... other expectations ...
EXPECT_EQ("good", MyProductionFunction(&foo)); // #5
} // #6
```
### Setting Default Actions {#OnCall}
gMock has a **built-in default action** for any function that returns `void`,
`bool`, a numeric value, or a pointer. In C++11, it will additionally returns
the default-constructed value, if one exists for the given type.
To customize the default action for functions with return type *`T`*:
```cpp
using ::testing::DefaultValue;
// Sets the default value to be returned. T must be CopyConstructible.
DefaultValue<T>::Set(value);
// Sets a factory. Will be invoked on demand. T must be MoveConstructible.
// T MakeT();
DefaultValue<T>::SetFactory(&MakeT);
// ... use the mocks ...
// Resets the default value.
DefaultValue<T>::Clear();
```
Example usage:
```cpp
// Sets the default action for return type std::unique_ptr<Buzz> to
// creating a new Buzz every time.
DefaultValue<std::unique_ptr<Buzz>>::SetFactory(
[] { return MakeUnique<Buzz>(AccessLevel::kInternal); });
// When this fires, the default action of MakeBuzz() will run, which
// will return a new Buzz object.
EXPECT_CALL(mock_buzzer_, MakeBuzz("hello")).Times(AnyNumber());
auto buzz1 = mock_buzzer_.MakeBuzz("hello");
auto buzz2 = mock_buzzer_.MakeBuzz("hello");
EXPECT_NE(nullptr, buzz1);
EXPECT_NE(nullptr, buzz2);
EXPECT_NE(buzz1, buzz2);
// Resets the default action for return type std::unique_ptr<Buzz>,
// to avoid interfere with other tests.
DefaultValue<std::unique_ptr<Buzz>>::Clear();
```
To customize the default action for a particular method of a specific mock
object, use `ON_CALL()`. `ON_CALL()` has a similar syntax to `EXPECT_CALL()`,
but it is used for setting default behaviors (when you do not require that the
mock method is called). See [here](cook_book.md#UseOnCall) for a more detailed
discussion.
```cpp
ON_CALL(mock-object, method(matchers))
.With(multi-argument-matcher) ?
.WillByDefault(action);
```
### Setting Expectations {#ExpectCall}
`EXPECT_CALL()` sets **expectations** on a mock method (How will it be called?
What will it do?):
```cpp
EXPECT_CALL(mock-object, method (matchers)?)
.With(multi-argument-matcher) ?
.Times(cardinality) ?
.InSequence(sequences) *
.After(expectations) *
.WillOnce(action) *
.WillRepeatedly(action) ?
.RetiresOnSaturation(); ?
```
For each item above, `?` means it can be used at most once, while `*` means it
can be used any number of times.
In order to pass, `EXPECT_CALL` must be used before the calls are actually made.
The `(matchers)` is a comma-separated list of matchers that correspond to each
of the arguments of `method`, and sets the expectation only for calls of
`method` that matches all of the matchers.
If `(matchers)` is omitted, the expectation is the same as if the matchers were
set to anything matchers (for example, `(_, _, _, _)` for a four-arg method).
If `Times()` is omitted, the cardinality is assumed to be:
* `Times(1)` when there is neither `WillOnce()` nor `WillRepeatedly()`;
* `Times(n)` when there are `n` `WillOnce()`s but no `WillRepeatedly()`, where
`n` >= 1; or
* `Times(AtLeast(n))` when there are `n` `WillOnce()`s and a
`WillRepeatedly()`, where `n` >= 0.
A method with no `EXPECT_CALL()` is free to be invoked *any number of times*,
and the default action will be taken each time.
### Matchers {#MatcherList}
<!-- GOOGLETEST_CM0020 DO NOT DELETE -->
A **matcher** matches a *single* argument. You can use it inside `ON_CALL()` or
`EXPECT_CALL()`, or use it to validate a value directly using two macros:
<!-- mdformat off(github rendering does not support multiline tables) -->
| Macro | Description |
| :----------------------------------- | :------------------------------------ |
| `EXPECT_THAT(actual_value, matcher)` | Asserts that `actual_value` matches `matcher`. |
| `ASSERT_THAT(actual_value, matcher)` | The same as `EXPECT_THAT(actual_value, matcher)`, except that it generates a **fatal** failure. |
<!-- mdformat on -->
Built-in matchers (where `argument` is the function argument, e.g.
`actual_value` in the example above, or when used in the context of
`EXPECT_CALL(mock_object, method(matchers))`, the arguments of `method`) are
divided into several categories:
#### Wildcard
Matcher | Description
:-------------------------- | :-----------------------------------------------
`_` | `argument` can be any value of the correct type.
`A<type>()` or `An<type>()` | `argument` can be any value of type `type`.
#### Generic Comparison
<!-- mdformat off(no multiline tables) -->
| Matcher | Description |
| :--------------------- | :-------------------------------------------------- |
| `Eq(value)` or `value` | `argument == value` |
| `Ge(value)` | `argument >= value` |
| `Gt(value)` | `argument > value` |
| `Le(value)` | `argument <= value` |
| `Lt(value)` | `argument < value` |
| `Ne(value)` | `argument != value` |
| `IsFalse()` | `argument` evaluates to `false` in a Boolean context. |
| `IsTrue()` | `argument` evaluates to `true` in a Boolean context. |
| `IsNull()` | `argument` is a `NULL` pointer (raw or smart). |
| `NotNull()` | `argument` is a non-null pointer (raw or smart). |
| `Optional(m)` | `argument` is `optional<>` that contains a value matching `m`. (For testing whether an `optional<>` is set, check for equality with `nullopt`. You may need to use `Eq(nullopt)` if the inner type doesn't have `==`.)|
| `VariantWith<T>(m)` | `argument` is `variant<>` that holds the alternative of type T with a value matching `m`. |
| `Ref(variable)` | `argument` is a reference to `variable`. |
| `TypedEq<type>(value)` | `argument` has type `type` and is equal to `value`. You may need to use this instead of `Eq(value)` when the mock function is overloaded. |
<!-- mdformat on -->
Except `Ref()`, these matchers make a *copy* of `value` in case it's modified or
destructed later. If the compiler complains that `value` doesn't have a public
copy constructor, try wrap it in `ByRef()`, e.g.
`Eq(ByRef(non_copyable_value))`. If you do that, make sure `non_copyable_value`
is not changed afterwards, or the meaning of your matcher will be changed.
#### Floating-Point Matchers {#FpMatchers}
<!-- mdformat off(no multiline tables) -->
| Matcher | Description |
| :------------------------------- | :--------------------------------- |
| `DoubleEq(a_double)` | `argument` is a `double` value approximately equal to `a_double`, treating two NaNs as unequal. |
| `FloatEq(a_float)` | `argument` is a `float` value approximately equal to `a_float`, treating two NaNs as unequal. |
| `NanSensitiveDoubleEq(a_double)` | `argument` is a `double` value approximately equal to `a_double`, treating two NaNs as equal. |
| `NanSensitiveFloatEq(a_float)` | `argument` is a `float` value approximately equal to `a_float`, treating two NaNs as equal. |
| `IsNan()` | `argument` is any floating-point type with a NaN value. |
<!-- mdformat on -->
The above matchers use ULP-based comparison (the same as used in googletest).
They automatically pick a reasonable error bound based on the absolute value of
the expected value. `DoubleEq()` and `FloatEq()` conform to the IEEE standard,
which requires comparing two NaNs for equality to return false. The
`NanSensitive*` version instead treats two NaNs as equal, which is often what a
user wants.
<!-- mdformat off(no multiline tables) -->
| Matcher | Description |
| :------------------------------------------------ | :----------------------- |
| `DoubleNear(a_double, max_abs_error)` | `argument` is a `double` value close to `a_double` (absolute error <= `max_abs_error`), treating two NaNs as unequal. |
| `FloatNear(a_float, max_abs_error)` | `argument` is a `float` value close to `a_float` (absolute error <= `max_abs_error`), treating two NaNs as unequal. |
| `NanSensitiveDoubleNear(a_double, max_abs_error)` | `argument` is a `double` value close to `a_double` (absolute error <= `max_abs_error`), treating two NaNs as equal. |
| `NanSensitiveFloatNear(a_float, max_abs_error)` | `argument` is a `float` value close to `a_float` (absolute error <= `max_abs_error`), treating two NaNs as equal. |
<!-- mdformat on -->
#### String Matchers
The `argument` can be either a C string or a C++ string object:
<!-- mdformat off(no multiline tables) -->
| Matcher | Description |
| :---------------------- | :------------------------------------------------- |
| `ContainsRegex(string)` | `argument` matches the given regular expression. |
| `EndsWith(suffix)` | `argument` ends with string `suffix`. |
| `HasSubstr(string)` | `argument` contains `string` as a sub-string. |
| `MatchesRegex(string)` | `argument` matches the given regular expression with the match starting at the first character and ending at the last character. |
| `StartsWith(prefix)` | `argument` starts with string `prefix`. |
| `StrCaseEq(string)` | `argument` is equal to `string`, ignoring case. |
| `StrCaseNe(string)` | `argument` is not equal to `string`, ignoring case. |
| `StrEq(string)` | `argument` is equal to `string`. |
| `StrNe(string)` | `argument` is not equal to `string`. |
<!-- mdformat on -->
`ContainsRegex()` and `MatchesRegex()` take ownership of the `RE` object. They
use the regular expression syntax defined
[here](../../googletest/docs/advanced.md#regular-expression-syntax). All of
these matchers, except `ContainsRegex()` and `MatchesRegex()` work for wide
strings as well.
#### Container Matchers
Most STL-style containers support `==`, so you can use `Eq(expected_container)`
or simply `expected_container` to match a container exactly. If you want to
write the elements in-line, match them more flexibly, or get more informative
messages, you can use:
<!-- mdformat off(no multiline tables) -->
| Matcher | Description |
| :---------------------------------------- | :------------------------------- |
| `BeginEndDistanceIs(m)` | `argument` is a container whose `begin()` and `end()` iterators are separated by a number of increments matching `m`. E.g. `BeginEndDistanceIs(2)` or `BeginEndDistanceIs(Lt(2))`. For containers that define a `size()` method, `SizeIs(m)` may be more efficient. |
| `ContainerEq(container)` | The same as `Eq(container)` except that the failure message also includes which elements are in one container but not the other. |
| `Contains(e)` | `argument` contains an element that matches `e`, which can be either a value or a matcher. |
| `Each(e)` | `argument` is a container where *every* element matches `e`, which can be either a value or a matcher. |
| `ElementsAre(e0, e1, ..., en)` | `argument` has `n + 1` elements, where the *i*-th element matches `ei`, which can be a value or a matcher. |
| `ElementsAreArray({e0, e1, ..., en})`, `ElementsAreArray(a_container)`, `ElementsAreArray(begin, end)`, `ElementsAreArray(array)`, or `ElementsAreArray(array, count)` | The same as `ElementsAre()` except that the expected element values/matchers come from an initializer list, STL-style container, iterator range, or C-style array. |
| `IsEmpty()` | `argument` is an empty container (`container.empty()`). |
| `IsSubsetOf({e0, e1, ..., en})`, `IsSubsetOf(a_container)`, `IsSubsetOf(begin, end)`, `IsSubsetOf(array)`, or `IsSubsetOf(array, count)` | `argument` matches `UnorderedElementsAre(x0, x1, ..., xk)` for some subset `{x0, x1, ..., xk}` of the expected matchers. |
| `IsSupersetOf({e0, e1, ..., en})`, `IsSupersetOf(a_container)`, `IsSupersetOf(begin, end)`, `IsSupersetOf(array)`, or `IsSupersetOf(array, count)` | Some subset of `argument` matches `UnorderedElementsAre(`expected matchers`)`. |
| `Pointwise(m, container)`, `Pointwise(m, {e0, e1, ..., en})` | `argument` contains the same number of elements as in `container`, and for all i, (the i-th element in `argument`, the i-th element in `container`) match `m`, which is a matcher on 2-tuples. E.g. `Pointwise(Le(), upper_bounds)` verifies that each element in `argument` doesn't exceed the corresponding element in `upper_bounds`. See more detail below. |
| `SizeIs(m)` | `argument` is a container whose size matches `m`. E.g. `SizeIs(2)` or `SizeIs(Lt(2))`. |
| `UnorderedElementsAre(e0, e1, ..., en)` | `argument` has `n + 1` elements, and under *some* permutation of the elements, each element matches an `ei` (for a different `i`), which can be a value or a matcher. |
| `UnorderedElementsAreArray({e0, e1, ..., en})`, `UnorderedElementsAreArray(a_container)`, `UnorderedElementsAreArray(begin, end)`, `UnorderedElementsAreArray(array)`, or `UnorderedElementsAreArray(array, count)` | The same as `UnorderedElementsAre()` except that the expected element values/matchers come from an initializer list, STL-style container, iterator range, or C-style array. |
| `UnorderedPointwise(m, container)`, `UnorderedPointwise(m, {e0, e1, ..., en})` | Like `Pointwise(m, container)`, but ignores the order of elements. |
| `WhenSorted(m)` | When `argument` is sorted using the `<` operator, it matches container matcher `m`. E.g. `WhenSorted(ElementsAre(1, 2, 3))` verifies that `argument` contains elements 1, 2, and 3, ignoring order. |
| `WhenSortedBy(comparator, m)` | The same as `WhenSorted(m)`, except that the given comparator instead of `<` is used to sort `argument`. E.g. `WhenSortedBy(std::greater(), ElementsAre(3, 2, 1))`. |
<!-- mdformat on -->
**Notes:**
* These matchers can also match:
1. a native array passed by reference (e.g. in `Foo(const int (&a)[5])`),
and
2. an array passed as a pointer and a count (e.g. in `Bar(const T* buffer,
int len)` -- see [Multi-argument Matchers](#MultiArgMatchers)).
* The array being matched may be multi-dimensional (i.e. its elements can be
arrays).
* `m` in `Pointwise(m, ...)` should be a matcher for `::std::tuple<T, U>`
where `T` and `U` are the element type of the actual container and the
expected container, respectively. For example, to compare two `Foo`
containers where `Foo` doesn't support `operator==`, one might write:
```cpp
using ::std::get;
MATCHER(FooEq, "") {
return std::get<0>(arg).Equals(std::get<1>(arg));
}
...
EXPECT_THAT(actual_foos, Pointwise(FooEq(), expected_foos));
```
#### Member Matchers
<!-- mdformat off(no multiline tables) -->
| Matcher | Description |
| :------------------------------ | :----------------------------------------- |
| `Field(&class::field, m)` | `argument.field` (or `argument->field` when `argument` is a plain pointer) matches matcher `m`, where `argument` is an object of type _class_. |
| `Key(e)` | `argument.first` matches `e`, which can be either a value or a matcher. E.g. `Contains(Key(Le(5)))` can verify that a `map` contains a key `<= 5`. |
| `Pair(m1, m2)` | `argument` is an `std::pair` whose `first` field matches `m1` and `second` field matches `m2`. |
| `Property(&class::property, m)` | `argument.property()` (or `argument->property()` when `argument` is a plain pointer) matches matcher `m`, where `argument` is an object of type _class_. |
<!-- mdformat on -->
#### Matching the Result of a Function, Functor, or Callback
<!-- mdformat off(no multiline tables) -->
| Matcher | Description |
| :--------------- | :------------------------------------------------ |
| `ResultOf(f, m)` | `f(argument)` matches matcher `m`, where `f` is a function or functor. |
<!-- mdformat on -->
#### Pointer Matchers
<!-- mdformat off(no multiline tables) -->
| Matcher | Description |
| :------------------------ | :---------------------------------------------- |
| `Pointee(m)` | `argument` (either a smart pointer or a raw pointer) points to a value that matches matcher `m`. |
| `WhenDynamicCastTo<T>(m)` | when `argument` is passed through `dynamic_cast<T>()`, it matches matcher `m`. |
<!-- mdformat on -->
<!-- GOOGLETEST_CM0026 DO NOT DELETE -->
<!-- GOOGLETEST_CM0027 DO NOT DELETE -->
#### Multi-argument Matchers {#MultiArgMatchers}
Technically, all matchers match a *single* value. A "multi-argument" matcher is
just one that matches a *tuple*. The following matchers can be used to match a
tuple `(x, y)`:
Matcher | Description
:------ | :----------
`Eq()` | `x == y`
`Ge()` | `x >= y`
`Gt()` | `x > y`
`Le()` | `x <= y`
`Lt()` | `x < y`
`Ne()` | `x != y`
You can use the following selectors to pick a subset of the arguments (or
reorder them) to participate in the matching:
<!-- mdformat off(no multiline tables) -->
| Matcher | Description |
| :------------------------- | :---------------------------------------------- |
| `AllArgs(m)` | Equivalent to `m`. Useful as syntactic sugar in `.With(AllArgs(m))`. |
| `Args<N1, N2, ..., Nk>(m)` | The tuple of the `k` selected (using 0-based indices) arguments matches `m`, e.g. `Args<1, 2>(Eq())`. |
<!-- mdformat on -->
#### Composite Matchers
You can make a matcher from one or more other matchers:
<!-- mdformat off(no multiline tables) -->
| Matcher | Description |
| :------------------------------- | :-------------------------------------- |
| `AllOf(m1, m2, ..., mn)` | `argument` matches all of the matchers `m1` to `mn`. |
| `AllOfArray({m0, m1, ..., mn})`, `AllOfArray(a_container)`, `AllOfArray(begin, end)`, `AllOfArray(array)`, or `AllOfArray(array, count)` | The same as `AllOf()` except that the matchers come from an initializer list, STL-style container, iterator range, or C-style array. |
| `AnyOf(m1, m2, ..., mn)` | `argument` matches at least one of the matchers `m1` to `mn`. |
| `AnyOfArray({m0, m1, ..., mn})`, `AnyOfArray(a_container)`, `AnyOfArray(begin, end)`, `AnyOfArray(array)`, or `AnyOfArray(array, count)` | The same as `AnyOf()` except that the matchers come from an initializer list, STL-style container, iterator range, or C-style array. |
| `Not(m)` | `argument` doesn't match matcher `m`. |
<!-- mdformat on -->
<!-- GOOGLETEST_CM0028 DO NOT DELETE -->
#### Adapters for Matchers
<!-- mdformat off(no multiline tables) -->
| Matcher | Description |
| :---------------------- | :------------------------------------ |
| `MatcherCast<T>(m)` | casts matcher `m` to type `Matcher<T>`. |
| `SafeMatcherCast<T>(m)` | [safely casts](cook_book.md#casting-matchers) matcher `m` to type `Matcher<T>`. |
| `Truly(predicate)` | `predicate(argument)` returns something considered by C++ to be true, where `predicate` is a function or functor. |
<!-- mdformat on -->
`AddressSatisfies(callback)` and `Truly(callback)` take ownership of `callback`,
which must be a permanent callback.
#### Using Matchers as Predicates {#MatchersAsPredicatesCheat}
<!-- mdformat off(no multiline tables) -->
| Matcher | Description |
| :---------------------------- | :------------------------------------------ |
| `Matches(m)(value)` | evaluates to `true` if `value` matches `m`. You can use `Matches(m)` alone as a unary functor. |
| `ExplainMatchResult(m, value, result_listener)` | evaluates to `true` if `value` matches `m`, explaining the result to `result_listener`. |
| `Value(value, m)` | evaluates to `true` if `value` matches `m`. |
<!-- mdformat on -->
#### Defining Matchers
<!-- mdformat off(no multiline tables) -->
| Matcher | Description |
| :----------------------------------- | :------------------------------------ |
| `MATCHER(IsEven, "") { return (arg % 2) == 0; }` | Defines a matcher `IsEven()` to match an even number. |
| `MATCHER_P(IsDivisibleBy, n, "") { *result_listener << "where the remainder is " << (arg % n); return (arg % n) == 0; }` | Defines a macher `IsDivisibleBy(n)` to match a number divisible by `n`. |
| `MATCHER_P2(IsBetween, a, b, std::string(negation ? "isn't" : "is") + " between " + PrintToString(a) + " and " + PrintToString(b)) { return a <= arg && arg <= b; }` | Defines a matcher `IsBetween(a, b)` to match a value in the range [`a`, `b`]. |
<!-- mdformat on -->
**Notes:**
1. The `MATCHER*` macros cannot be used inside a function or class.
2. The matcher body must be *purely functional* (i.e. it cannot have any side
effect, and the result must not depend on anything other than the value
being matched and the matcher parameters).
3. You can use `PrintToString(x)` to convert a value `x` of any type to a
string.
### Actions {#ActionList}
**Actions** specify what a mock function should do when invoked.
#### Returning a Value
<!-- mdformat off(no multiline tables) -->
| | |
| :-------------------------------- | :-------------------------------------------- |
| `Return()` | Return from a `void` mock function. |
| `Return(value)` | Return `value`. If the type of `value` is different to the mock function's return type, `value` is converted to the latter type <i>at the time the expectation is set</i>, not when the action is executed. |
| `ReturnArg<N>()` | Return the `N`-th (0-based) argument. |
| `ReturnNew<T>(a1, ..., ak)` | Return `new T(a1, ..., ak)`; a different object is created each time. |
| `ReturnNull()` | Return a null pointer. |
| `ReturnPointee(ptr)` | Return the value pointed to by `ptr`. |
| `ReturnRef(variable)` | Return a reference to `variable`. |
| `ReturnRefOfCopy(value)` | Return a reference to a copy of `value`; the copy lives as long as the action. |
| `ReturnRoundRobin({a1, ..., ak})` | Each call will return the next `ai` in the list, starting at the beginning when the end of the list is reached. |
<!-- mdformat on -->
#### Side Effects
<!-- mdformat off(no multiline tables) -->
| | |
| :--------------------------------- | :-------------------------------------- |
| `Assign(&variable, value)` | Assign `value` to variable. |
| `DeleteArg<N>()` | Delete the `N`-th (0-based) argument, which must be a pointer. |
| `SaveArg<N>(pointer)` | Save the `N`-th (0-based) argument to `*pointer`. |
| `SaveArgPointee<N>(pointer)` | Save the value pointed to by the `N`-th (0-based) argument to `*pointer`. |
| `SetArgReferee<N>(value)` | Assign value to the variable referenced by the `N`-th (0-based) argument. |
| `SetArgPointee<N>(value)` | Assign `value` to the variable pointed by the `N`-th (0-based) argument. |
| `SetArgumentPointee<N>(value)` | Same as `SetArgPointee<N>(value)`. Deprecated. Will be removed in v1.7.0. |
| `SetArrayArgument<N>(first, last)` | Copies the elements in source range [`first`, `last`) to the array pointed to by the `N`-th (0-based) argument, which can be either a pointer or an iterator. The action does not take ownership of the elements in the source range. |
| `SetErrnoAndReturn(error, value)` | Set `errno` to `error` and return `value`. |
| `Throw(exception)` | Throws the given exception, which can be any copyable value. Available since v1.1.0. |
<!-- mdformat on -->
#### Using a Function, Functor, or Lambda as an Action
In the following, by "callable" we mean a free function, `std::function`,
functor, or lambda.
<!-- mdformat off(no multiline tables) -->
| | |
| :---------------------------------- | :------------------------------------- |
| `f` | Invoke f with the arguments passed to the mock function, where f is a callable. |
| `Invoke(f)` | Invoke `f` with the arguments passed to the mock function, where `f` can be a global/static function or a functor. |
| `Invoke(object_pointer, &class::method)` | Invoke the method on the object with the arguments passed to the mock function. |
| `InvokeWithoutArgs(f)` | Invoke `f`, which can be a global/static function or a functor. `f` must take no arguments. |
| `InvokeWithoutArgs(object_pointer, &class::method)` | Invoke the method on the object, which takes no arguments. |
| `InvokeArgument<N>(arg1, arg2, ..., argk)` | Invoke the mock function's `N`-th (0-based) argument, which must be a function or a functor, with the `k` arguments. |
<!-- mdformat on -->
The return value of the invoked function is used as the return value of the
action.
When defining a callable to be used with `Invoke*()`, you can declare any unused
parameters as `Unused`:
```cpp
using ::testing::Invoke;
double Distance(Unused, double x, double y) { return sqrt(x*x + y*y); }
...
EXPECT_CALL(mock, Foo("Hi", _, _)).WillOnce(Invoke(Distance));
```
`Invoke(callback)` and `InvokeWithoutArgs(callback)` take ownership of
`callback`, which must be permanent. The type of `callback` must be a base
callback type instead of a derived one, e.g.
```cpp
BlockingClosure* done = new BlockingClosure;
... Invoke(done) ...; // This won't compile!
Closure* done2 = new BlockingClosure;
... Invoke(done2) ...; // This works.
```
In `InvokeArgument<N>(...)`, if an argument needs to be passed by reference,
wrap it inside `ByRef()`. For example,
```cpp
using ::testing::ByRef;
using ::testing::InvokeArgument;
...
InvokeArgument<2>(5, string("Hi"), ByRef(foo))
```
calls the mock function's #2 argument, passing to it `5` and `string("Hi")` by
value, and `foo` by reference.
#### Default Action
<!-- mdformat off(no multiline tables) -->
| Matcher | Description |
| :------------ | :----------------------------------------------------- |
| `DoDefault()` | Do the default action (specified by `ON_CALL()` or the built-in one). |
<!-- mdformat on -->
**Note:** due to technical reasons, `DoDefault()` cannot be used inside a
composite action - trying to do so will result in a run-time error.
<!-- GOOGLETEST_CM0032 DO NOT DELETE -->
#### Composite Actions
<!-- mdformat off(no multiline tables) -->
| | |
| :----------------------------- | :------------------------------------------ |
| `DoAll(a1, a2, ..., an)` | Do all actions `a1` to `an` and return the result of `an` in each invocation. The first `n - 1` sub-actions must return void. |
| `IgnoreResult(a)` | Perform action `a` and ignore its result. `a` must not return void. |
| `WithArg<N>(a)` | Pass the `N`-th (0-based) argument of the mock function to action `a` and perform it. |
| `WithArgs<N1, N2, ..., Nk>(a)` | Pass the selected (0-based) arguments of the mock function to action `a` and perform it. |
| `WithoutArgs(a)` | Perform action `a` without any arguments. |
<!-- mdformat on -->
#### Defining Actions
<!-- mdformat off(no multiline tables) -->
| | |
| :--------------------------------- | :-------------------------------------- |
| `ACTION(Sum) { return arg0 + arg1; }` | Defines an action `Sum()` to return the sum of the mock function's argument #0 and #1. |
| `ACTION_P(Plus, n) { return arg0 + n; }` | Defines an action `Plus(n)` to return the sum of the mock function's argument #0 and `n`. |
| `ACTION_Pk(Foo, p1, ..., pk) { statements; }` | Defines a parameterized action `Foo(p1, ..., pk)` to execute the given `statements`. |
<!-- mdformat on -->
The `ACTION*` macros cannot be used inside a function or class.
### Cardinalities {#CardinalityList}
These are used in `Times()` to specify how many times a mock function will be
called:
<!-- mdformat off(no multiline tables) -->
| | |
| :---------------- | :----------------------------------------------------- |
| `AnyNumber()` | The function can be called any number of times. |
| `AtLeast(n)` | The call is expected at least `n` times. |
| `AtMost(n)` | The call is expected at most `n` times. |
| `Between(m, n)` | The call is expected between `m` and `n` (inclusive) times. |
| `Exactly(n) or n` | The call is expected exactly `n` times. In particular, the call should never happen when `n` is 0. |
<!-- mdformat on -->
### Expectation Order
By default, the expectations can be matched in *any* order. If some or all
expectations must be matched in a given order, there are two ways to specify it.
They can be used either independently or together.
#### The After Clause {#AfterClause}
```cpp
using ::testing::Expectation;
...
Expectation init_x = EXPECT_CALL(foo, InitX());
Expectation init_y = EXPECT_CALL(foo, InitY());
EXPECT_CALL(foo, Bar())
.After(init_x, init_y);
```
says that `Bar()` can be called only after both `InitX()` and `InitY()` have
been called.
If you don't know how many pre-requisites an expectation has when you write it,
you can use an `ExpectationSet` to collect them:
```cpp
using ::testing::ExpectationSet;
...
ExpectationSet all_inits;
for (int i = 0; i < element_count; i++) {
all_inits += EXPECT_CALL(foo, InitElement(i));
}
EXPECT_CALL(foo, Bar())
.After(all_inits);
```
says that `Bar()` can be called only after all elements have been initialized
(but we don't care about which elements get initialized before the others).
Modifying an `ExpectationSet` after using it in an `.After()` doesn't affect the
meaning of the `.After()`.
#### Sequences {#UsingSequences}
When you have a long chain of sequential expectations, it's easier to specify
the order using **sequences**, which don't require you to given each expectation
in the chain a different name. *All expected calls* in the same sequence must
occur in the order they are specified.
```cpp
using ::testing::Return;
using ::testing::Sequence;
Sequence s1, s2;
...
EXPECT_CALL(foo, Reset())
.InSequence(s1, s2)
.WillOnce(Return(true));
EXPECT_CALL(foo, GetSize())
.InSequence(s1)
.WillOnce(Return(1));
EXPECT_CALL(foo, Describe(A<const char*>()))
.InSequence(s2)
.WillOnce(Return("dummy"));
```
says that `Reset()` must be called before *both* `GetSize()` *and* `Describe()`,
and the latter two can occur in any order.
To put many expectations in a sequence conveniently:
```cpp
using ::testing::InSequence;
{
InSequence seq;
EXPECT_CALL(...)...;
EXPECT_CALL(...)...;
...
EXPECT_CALL(...)...;
}
```
says that all expected calls in the scope of `seq` must occur in strict order.
The name `seq` is irrelevant.
### Verifying and Resetting a Mock
gMock will verify the expectations on a mock object when it is destructed, or
you can do it earlier:
```cpp
using ::testing::Mock;
...
// Verifies and removes the expectations on mock_obj;
// returns true if and only if successful.
Mock::VerifyAndClearExpectations(&mock_obj);
...
// Verifies and removes the expectations on mock_obj;
// also removes the default actions set by ON_CALL();
// returns true if and only if successful.
Mock::VerifyAndClear(&mock_obj);
```
You can also tell gMock that a mock object can be leaked and doesn't need to be
verified:
```cpp
Mock::AllowLeak(&mock_obj);
```
### Mock Classes
gMock defines a convenient mock class template
```cpp
class MockFunction<R(A1, ..., An)> {
public:
MOCK_METHOD(R, Call, (A1, ..., An));
};
```
See this [recipe](cook_book.md#using-check-points) for one application of it.
### Flags
<!-- mdformat off(no multiline tables) -->
| Flag | Description |
| :----------------------------- | :---------------------------------------- |
| `--gmock_catch_leaked_mocks=0` | Don't report leaked mock objects as failures. |
| `--gmock_verbose=LEVEL` | Sets the default verbosity level (`info`, `warning`, or `error`) of Google Mock messages. |
<!-- mdformat on -->

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## gMock for Dummies {#GMockForDummies}
<!-- GOOGLETEST_CM0013 DO NOT DELETE -->
### What Is gMock?
When you write a prototype or test, often it's not feasible or wise to rely on
real objects entirely. A **mock object** implements the same interface as a real
object (so it can be used as one), but lets you specify at run time how it will
be used and what it should do (which methods will be called? in which order? how
many times? with what arguments? what will they return? etc).
**Note:** It is easy to confuse the term *fake objects* with mock objects. Fakes
and mocks actually mean very different things in the Test-Driven Development
(TDD) community:
* **Fake** objects have working implementations, but usually take some
shortcut (perhaps to make the operations less expensive), which makes them
not suitable for production. An in-memory file system would be an example of
a fake.
* **Mocks** are objects pre-programmed with *expectations*, which form a
specification of the calls they are expected to receive.
If all this seems too abstract for you, don't worry - the most important thing
to remember is that a mock allows you to check the *interaction* between itself
and code that uses it. The difference between fakes and mocks shall become much
clearer once you start to use mocks.
**gMock** is a library (sometimes we also call it a "framework" to make it sound
cool) for creating mock classes and using them. It does to C++ what
jMock/EasyMock does to Java (well, more or less).
When using gMock,
1. first, you use some simple macros to describe the interface you want to
mock, and they will expand to the implementation of your mock class;
2. next, you create some mock objects and specify its expectations and behavior
using an intuitive syntax;
3. then you exercise code that uses the mock objects. gMock will catch any
violation to the expectations as soon as it arises.
### Why gMock?
While mock objects help you remove unnecessary dependencies in tests and make
them fast and reliable, using mocks manually in C++ is *hard*:
* Someone has to implement the mocks. The job is usually tedious and
error-prone. No wonder people go great distance to avoid it.
* The quality of those manually written mocks is a bit, uh, unpredictable. You
may see some really polished ones, but you may also see some that were
hacked up in a hurry and have all sorts of ad hoc restrictions.
* The knowledge you gained from using one mock doesn't transfer to the next
one.
In contrast, Java and Python programmers have some fine mock frameworks (jMock,
EasyMock, [Mox](http://wtf/mox), etc), which automate the creation of mocks. As
a result, mocking is a proven effective technique and widely adopted practice in
those communities. Having the right tool absolutely makes the difference.
gMock was built to help C++ programmers. It was inspired by jMock and EasyMock,
but designed with C++'s specifics in mind. It is your friend if any of the
following problems is bothering you:
* You are stuck with a sub-optimal design and wish you had done more
prototyping before it was too late, but prototyping in C++ is by no means
"rapid".
* Your tests are slow as they depend on too many libraries or use expensive
resources (e.g. a database).
* Your tests are brittle as some resources they use are unreliable (e.g. the
network).
* You want to test how your code handles a failure (e.g. a file checksum
error), but it's not easy to cause one.
* You need to make sure that your module interacts with other modules in the
right way, but it's hard to observe the interaction; therefore you resort to
observing the side effects at the end of the action, but it's awkward at
best.
* You want to "mock out" your dependencies, except that they don't have mock
implementations yet; and, frankly, you aren't thrilled by some of those
hand-written mocks.
We encourage you to use gMock as
* a *design* tool, for it lets you experiment with your interface design early
and often. More iterations lead to better designs!
* a *testing* tool to cut your tests' outbound dependencies and probe the
interaction between your module and its collaborators.
### Getting Started
gMock is bundled with googletest.
### A Case for Mock Turtles
Let's look at an example. Suppose you are developing a graphics program that
relies on a [LOGO](http://en.wikipedia.org/wiki/Logo_programming_language)-like
API for drawing. How would you test that it does the right thing? Well, you can
run it and compare the screen with a golden screen snapshot, but let's admit it:
tests like this are expensive to run and fragile (What if you just upgraded to a
shiny new graphics card that has better anti-aliasing? Suddenly you have to
update all your golden images.). It would be too painful if all your tests are
like this. Fortunately, you learned about
[Dependency Injection](http://en.wikipedia.org/wiki/Dependency_injection) and know the right thing
to do: instead of having your application talk to the system API directly, wrap
the API in an interface (say, `Turtle`) and code to that interface:
```cpp
class Turtle {
...
virtual ~Turtle() {};
virtual void PenUp() = 0;
virtual void PenDown() = 0;
virtual void Forward(int distance) = 0;
virtual void Turn(int degrees) = 0;
virtual void GoTo(int x, int y) = 0;
virtual int GetX() const = 0;
virtual int GetY() const = 0;
};
```
(Note that the destructor of `Turtle` **must** be virtual, as is the case for
**all** classes you intend to inherit from - otherwise the destructor of the
derived class will not be called when you delete an object through a base
pointer, and you'll get corrupted program states like memory leaks.)
You can control whether the turtle's movement will leave a trace using `PenUp()`
and `PenDown()`, and control its movement using `Forward()`, `Turn()`, and
`GoTo()`. Finally, `GetX()` and `GetY()` tell you the current position of the
turtle.
Your program will normally use a real implementation of this interface. In
tests, you can use a mock implementation instead. This allows you to easily
check what drawing primitives your program is calling, with what arguments, and
in which order. Tests written this way are much more robust (they won't break
because your new machine does anti-aliasing differently), easier to read and
maintain (the intent of a test is expressed in the code, not in some binary
images), and run *much, much faster*.
### Writing the Mock Class
If you are lucky, the mocks you need to use have already been implemented by
some nice people. If, however, you find yourself in the position to write a mock
class, relax - gMock turns this task into a fun game! (Well, almost.)
#### How to Define It
Using the `Turtle` interface as example, here are the simple steps you need to
follow:
* Derive a class `MockTurtle` from `Turtle`.
* Take a *virtual* function of `Turtle` (while it's possible to
[mock non-virtual methods using templates](cook_book.md#MockingNonVirtualMethods),
it's much more involved).
* In the `public:` section of the child class, write `MOCK_METHOD();`
* Now comes the fun part: you take the function signature, cut-and-paste it
into the macro, and add two commas - one between the return type and the
name, another between the name and the argument list.
* If you're mocking a const method, add a 4th parameter containing `(const)`
(the parentheses are required).
* Since you're overriding a virtual method, we suggest adding the `override`
keyword. For const methods the 4th parameter becomes `(const, override)`,
for non-const methods just `(override)`. This isn't mandatory.
* Repeat until all virtual functions you want to mock are done. (It goes
without saying that *all* pure virtual methods in your abstract class must
be either mocked or overridden.)
After the process, you should have something like:
```cpp
#include "gmock/gmock.h" // Brings in gMock.
class MockTurtle : public Turtle {
public:
...
MOCK_METHOD(void, PenUp, (), (override));
MOCK_METHOD(void, PenDown, (), (override));
MOCK_METHOD(void, Forward, (int distance), (override));
MOCK_METHOD(void, Turn, (int degrees), (override));
MOCK_METHOD(void, GoTo, (int x, int y), (override));
MOCK_METHOD(int, GetX, (), (const, override));
MOCK_METHOD(int, GetY, (), (const, override));
};
```
You don't need to define these mock methods somewhere else - the `MOCK_METHOD`
macro will generate the definitions for you. It's that simple!
#### Where to Put It
When you define a mock class, you need to decide where to put its definition.
Some people put it in a `_test.cc`. This is fine when the interface being mocked
(say, `Foo`) is owned by the same person or team. Otherwise, when the owner of
`Foo` changes it, your test could break. (You can't really expect `Foo`'s
maintainer to fix every test that uses `Foo`, can you?)
So, the rule of thumb is: if you need to mock `Foo` and it's owned by others,
define the mock class in `Foo`'s package (better, in a `testing` sub-package
such that you can clearly separate production code and testing utilities), put
it in a `.h` and a `cc_library`. Then everyone can reference them from their
tests. If `Foo` ever changes, there is only one copy of `MockFoo` to change, and
only tests that depend on the changed methods need to be fixed.
Another way to do it: you can introduce a thin layer `FooAdaptor` on top of
`Foo` and code to this new interface. Since you own `FooAdaptor`, you can absorb
changes in `Foo` much more easily. While this is more work initially, carefully
choosing the adaptor interface can make your code easier to write and more
readable (a net win in the long run), as you can choose `FooAdaptor` to fit your
specific domain much better than `Foo` does.
<!-- GOOGLETEST_CM0029 DO NOT DELETE -->
### Using Mocks in Tests
Once you have a mock class, using it is easy. The typical work flow is:
1. Import the gMock names from the `testing` namespace such that you can use
them unqualified (You only have to do it once per file). Remember that
namespaces are a good idea.
2. Create some mock objects.
3. Specify your expectations on them (How many times will a method be called?
With what arguments? What should it do? etc.).
4. Exercise some code that uses the mocks; optionally, check the result using
googletest assertions. If a mock method is called more than expected or with
wrong arguments, you'll get an error immediately.
5. When a mock is destructed, gMock will automatically check whether all
expectations on it have been satisfied.
Here's an example:
```cpp
#include "path/to/mock-turtle.h"
#include "gmock/gmock.h"
#include "gtest/gtest.h"
using ::testing::AtLeast; // #1
TEST(PainterTest, CanDrawSomething) {
MockTurtle turtle; // #2
EXPECT_CALL(turtle, PenDown()) // #3
.Times(AtLeast(1));
Painter painter(&turtle); // #4
EXPECT_TRUE(painter.DrawCircle(0, 0, 10)); // #5
}
```
As you might have guessed, this test checks that `PenDown()` is called at least
once. If the `painter` object didn't call this method, your test will fail with
a message like this:
```text
path/to/my_test.cc:119: Failure
Actual function call count doesn't match this expectation:
Actually: never called;
Expected: called at least once.
Stack trace:
...
```
**Tip 1:** If you run the test from an Emacs buffer, you can hit <Enter> on the
line number to jump right to the failed expectation.
**Tip 2:** If your mock objects are never deleted, the final verification won't
happen. Therefore it's a good idea to turn on the heap checker in your tests
when you allocate mocks on the heap. You get that automatically if you use the
`gtest_main` library already.
**Important note:** gMock requires expectations to be set **before** the mock
functions are called, otherwise the behavior is **undefined**. In particular,
you mustn't interleave `EXPECT_CALL()s` and calls to the mock functions.
This means `EXPECT_CALL()` should be read as expecting that a call will occur
*in the future*, not that a call has occurred. Why does gMock work like that?
Well, specifying the expectation beforehand allows gMock to report a violation
as soon as it rises, when the context (stack trace, etc) is still available.
This makes debugging much easier.
Admittedly, this test is contrived and doesn't do much. You can easily achieve
the same effect without using gMock. However, as we shall reveal soon, gMock
allows you to do *so much more* with the mocks.
### Setting Expectations
The key to using a mock object successfully is to set the *right expectations*
on it. If you set the expectations too strict, your test will fail as the result
of unrelated changes. If you set them too loose, bugs can slip through. You want
to do it just right such that your test can catch exactly the kind of bugs you
intend it to catch. gMock provides the necessary means for you to do it "just
right."
#### General Syntax
In gMock we use the `EXPECT_CALL()` macro to set an expectation on a mock
method. The general syntax is:
```cpp
EXPECT_CALL(mock_object, method(matchers))
.Times(cardinality)
.WillOnce(action)
.WillRepeatedly(action);
```
The macro has two arguments: first the mock object, and then the method and its
arguments. Note that the two are separated by a comma (`,`), not a period (`.`).
(Why using a comma? The answer is that it was necessary for technical reasons.)
If the method is not overloaded, the macro can also be called without matchers:
```cpp
EXPECT_CALL(mock_object, non-overloaded-method)
.Times(cardinality)
.WillOnce(action)
.WillRepeatedly(action);
```
This syntax allows the test writer to specify "called with any arguments"
without explicitly specifying the number or types of arguments. To avoid
unintended ambiguity, this syntax may only be used for methods which are not
overloaded
Either form of the macro can be followed by some optional *clauses* that provide
more information about the expectation. We'll discuss how each clause works in
the coming sections.
This syntax is designed to make an expectation read like English. For example,
you can probably guess that
```cpp
using ::testing::Return;
...
EXPECT_CALL(turtle, GetX())
.Times(5)
.WillOnce(Return(100))
.WillOnce(Return(150))
.WillRepeatedly(Return(200));
```
says that the `turtle` object's `GetX()` method will be called five times, it
will return 100 the first time, 150 the second time, and then 200 every time.
Some people like to call this style of syntax a Domain-Specific Language (DSL).
**Note:** Why do we use a macro to do this? Well it serves two purposes: first
it makes expectations easily identifiable (either by `gsearch` or by a human
reader), and second it allows gMock to include the source file location of a
failed expectation in messages, making debugging easier.
#### Matchers: What Arguments Do We Expect?
When a mock function takes arguments, we may specify what arguments we are
expecting, for example:
```cpp
// Expects the turtle to move forward by 100 units.
EXPECT_CALL(turtle, Forward(100));
```
Oftentimes you do not want to be too specific. Remember that talk about tests
being too rigid? Over specification leads to brittle tests and obscures the
intent of tests. Therefore we encourage you to specify only what's necessary—no
more, no less. If you aren't interested in the value of an argument, write `_`
as the argument, which means "anything goes":
```cpp
using ::testing::_;
...
// Expects that the turtle jumps to somewhere on the x=50 line.
EXPECT_CALL(turtle, GoTo(50, _));
```
`_` is an instance of what we call **matchers**. A matcher is like a predicate
and can test whether an argument is what we'd expect. You can use a matcher
inside `EXPECT_CALL()` wherever a function argument is expected. `_` is a
convenient way of saying "any value".
In the above examples, `100` and `50` are also matchers; implicitly, they are
the same as `Eq(100)` and `Eq(50)`, which specify that the argument must be
equal (using `operator==`) to the matcher argument. There are many
[built-in matchers](#MatcherList) for common types (as well as
[custom matchers](cook_book.md#NewMatchers)); for example:
```cpp
using ::testing::Ge;
...
// Expects the turtle moves forward by at least 100.
EXPECT_CALL(turtle, Forward(Ge(100)));
```
If you don't care about *any* arguments, rather than specify `_` for each of
them you may instead omit the parameter list:
```cpp
// Expects the turtle to move forward.
EXPECT_CALL(turtle, Forward);
// Expects the turtle to jump somewhere.
EXPECT_CALL(turtle, GoTo);
```
This works for all non-overloaded methods; if a method is overloaded, you need
to help gMock resolve which overload is expected by specifying the number of
arguments and possibly also the
[types of the arguments](cook_book.md#SelectOverload).
#### Cardinalities: How Many Times Will It Be Called?
The first clause we can specify following an `EXPECT_CALL()` is `Times()`. We
call its argument a **cardinality** as it tells *how many times* the call should
occur. It allows us to repeat an expectation many times without actually writing
it as many times. More importantly, a cardinality can be "fuzzy", just like a
matcher can be. This allows a user to express the intent of a test exactly.
An interesting special case is when we say `Times(0)`. You may have guessed - it
means that the function shouldn't be called with the given arguments at all, and
gMock will report a googletest failure whenever the function is (wrongfully)
called.
We've seen `AtLeast(n)` as an example of fuzzy cardinalities earlier. For the
list of built-in cardinalities you can use, see
[here](cheat_sheet.md#CardinalityList).
The `Times()` clause can be omitted. **If you omit `Times()`, gMock will infer
the cardinality for you.** The rules are easy to remember:
* If **neither** `WillOnce()` **nor** `WillRepeatedly()` is in the
`EXPECT_CALL()`, the inferred cardinality is `Times(1)`.
* If there are *n* `WillOnce()`'s but **no** `WillRepeatedly()`, where *n* >=
1, the cardinality is `Times(n)`.
* If there are *n* `WillOnce()`'s and **one** `WillRepeatedly()`, where *n* >=
0, the cardinality is `Times(AtLeast(n))`.
**Quick quiz:** what do you think will happen if a function is expected to be
called twice but actually called four times?
#### Actions: What Should It Do?
Remember that a mock object doesn't really have a working implementation? We as
users have to tell it what to do when a method is invoked. This is easy in
gMock.
First, if the return type of a mock function is a built-in type or a pointer,
the function has a **default action** (a `void` function will just return, a
`bool` function will return `false`, and other functions will return 0). In
addition, in C++ 11 and above, a mock function whose return type is
default-constructible (i.e. has a default constructor) has a default action of
returning a default-constructed value. If you don't say anything, this behavior
will be used.
Second, if a mock function doesn't have a default action, or the default action
doesn't suit you, you can specify the action to be taken each time the
expectation matches using a series of `WillOnce()` clauses followed by an
optional `WillRepeatedly()`. For example,
```cpp
using ::testing::Return;
...
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(100))
.WillOnce(Return(200))
.WillOnce(Return(300));
```
says that `turtle.GetX()` will be called *exactly three times* (gMock inferred
this from how many `WillOnce()` clauses we've written, since we didn't
explicitly write `Times()`), and will return 100, 200, and 300 respectively.
```cpp
using ::testing::Return;
...
EXPECT_CALL(turtle, GetY())
.WillOnce(Return(100))
.WillOnce(Return(200))
.WillRepeatedly(Return(300));
```
says that `turtle.GetY()` will be called *at least twice* (gMock knows this as
we've written two `WillOnce()` clauses and a `WillRepeatedly()` while having no
explicit `Times()`), will return 100 and 200 respectively the first two times,
and 300 from the third time on.
Of course, if you explicitly write a `Times()`, gMock will not try to infer the
cardinality itself. What if the number you specified is larger than there are
`WillOnce()` clauses? Well, after all `WillOnce()`s are used up, gMock will do
the *default* action for the function every time (unless, of course, you have a
`WillRepeatedly()`.).
What can we do inside `WillOnce()` besides `Return()`? You can return a
reference using `ReturnRef(*variable*)`, or invoke a pre-defined function, among
[others](cook_book.md#using-actions).
**Important note:** The `EXPECT_CALL()` statement evaluates the action clause
only once, even though the action may be performed many times. Therefore you
must be careful about side effects. The following may not do what you want:
```cpp
using ::testing::Return;
...
int n = 100;
EXPECT_CALL(turtle, GetX())
.Times(4)
.WillRepeatedly(Return(n++));
```
Instead of returning 100, 101, 102, ..., consecutively, this mock function will
always return 100 as `n++` is only evaluated once. Similarly, `Return(new Foo)`
will create a new `Foo` object when the `EXPECT_CALL()` is executed, and will
return the same pointer every time. If you want the side effect to happen every
time, you need to define a custom action, which we'll teach in the
[cook book](http://<!-- GOOGLETEST_CM0012 DO NOT DELETE -->).
Time for another quiz! What do you think the following means?
```cpp
using ::testing::Return;
...
EXPECT_CALL(turtle, GetY())
.Times(4)
.WillOnce(Return(100));
```
Obviously `turtle.GetY()` is expected to be called four times. But if you think
it will return 100 every time, think twice! Remember that one `WillOnce()`
clause will be consumed each time the function is invoked and the default action
will be taken afterwards. So the right answer is that `turtle.GetY()` will
return 100 the first time, but **return 0 from the second time on**, as
returning 0 is the default action for `int` functions.
#### Using Multiple Expectations {#MultiExpectations}
So far we've only shown examples where you have a single expectation. More
realistically, you'll specify expectations on multiple mock methods which may be
from multiple mock objects.
By default, when a mock method is invoked, gMock will search the expectations in
the **reverse order** they are defined, and stop when an active expectation that
matches the arguments is found (you can think of it as "newer rules override
older ones."). If the matching expectation cannot take any more calls, you will
get an upper-bound-violated failure. Here's an example:
```cpp
using ::testing::_;
...
EXPECT_CALL(turtle, Forward(_)); // #1
EXPECT_CALL(turtle, Forward(10)) // #2
.Times(2);
```
If `Forward(10)` is called three times in a row, the third time it will be an
error, as the last matching expectation (#2) has been saturated. If, however,
the third `Forward(10)` call is replaced by `Forward(20)`, then it would be OK,
as now #1 will be the matching expectation.
**Note:** Why does gMock search for a match in the *reverse* order of the
expectations? The reason is that this allows a user to set up the default
expectations in a mock object's constructor or the test fixture's set-up phase
and then customize the mock by writing more specific expectations in the test
body. So, if you have two expectations on the same method, you want to put the
one with more specific matchers **after** the other, or the more specific rule
would be shadowed by the more general one that comes after it.
**Tip:** It is very common to start with a catch-all expectation for a method
and `Times(AnyNumber())` (omitting arguments, or with `_` for all arguments, if
overloaded). This makes any calls to the method expected. This is not necessary
for methods that are not mentioned at all (these are "uninteresting"), but is
useful for methods that have some expectations, but for which other calls are
ok. See
[Understanding Uninteresting vs Unexpected Calls](cook_book.md#uninteresting-vs-unexpected).
#### Ordered vs Unordered Calls {#OrderedCalls}
By default, an expectation can match a call even though an earlier expectation
hasn't been satisfied. In other words, the calls don't have to occur in the
order the expectations are specified.
Sometimes, you may want all the expected calls to occur in a strict order. To
say this in gMock is easy:
```cpp
using ::testing::InSequence;
...
TEST(FooTest, DrawsLineSegment) {
...
{
InSequence seq;
EXPECT_CALL(turtle, PenDown());
EXPECT_CALL(turtle, Forward(100));
EXPECT_CALL(turtle, PenUp());
}
Foo();
}
```
By creating an object of type `InSequence`, all expectations in its scope are
put into a *sequence* and have to occur *sequentially*. Since we are just
relying on the constructor and destructor of this object to do the actual work,
its name is really irrelevant.
In this example, we test that `Foo()` calls the three expected functions in the
order as written. If a call is made out-of-order, it will be an error.
(What if you care about the relative order of some of the calls, but not all of
them? Can you specify an arbitrary partial order? The answer is ... yes! The
details can be found [here](cook_book.md#OrderedCalls).)
#### All Expectations Are Sticky (Unless Said Otherwise) {#StickyExpectations}
Now let's do a quick quiz to see how well you can use this mock stuff already.
How would you test that the turtle is asked to go to the origin *exactly twice*
(you want to ignore any other instructions it receives)?
After you've come up with your answer, take a look at ours and compare notes
(solve it yourself first - don't cheat!):
```cpp
using ::testing::_;
using ::testing::AnyNumber;
...
EXPECT_CALL(turtle, GoTo(_, _)) // #1
.Times(AnyNumber());
EXPECT_CALL(turtle, GoTo(0, 0)) // #2
.Times(2);
```
Suppose `turtle.GoTo(0, 0)` is called three times. In the third time, gMock will
see that the arguments match expectation #2 (remember that we always pick the
last matching expectation). Now, since we said that there should be only two
such calls, gMock will report an error immediately. This is basically what we've
told you in the [Using Multiple Expectations](#MultiExpectations) section above.
This example shows that **expectations in gMock are "sticky" by default**, in
the sense that they remain active even after we have reached their invocation
upper bounds. This is an important rule to remember, as it affects the meaning
of the spec, and is **different** to how it's done in many other mocking
frameworks (Why'd we do that? Because we think our rule makes the common cases
easier to express and understand.).
Simple? Let's see if you've really understood it: what does the following code
say?
```cpp
using ::testing::Return;
...
for (int i = n; i > 0; i--) {
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(10*i));
}
```
If you think it says that `turtle.GetX()` will be called `n` times and will
return 10, 20, 30, ..., consecutively, think twice! The problem is that, as we
said, expectations are sticky. So, the second time `turtle.GetX()` is called,
the last (latest) `EXPECT_CALL()` statement will match, and will immediately
lead to an "upper bound violated" error - this piece of code is not very useful!
One correct way of saying that `turtle.GetX()` will return 10, 20, 30, ..., is
to explicitly say that the expectations are *not* sticky. In other words, they
should *retire* as soon as they are saturated:
```cpp
using ::testing::Return;
...
for (int i = n; i > 0; i--) {
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(10*i))
.RetiresOnSaturation();
}
```
And, there's a better way to do it: in this case, we expect the calls to occur
in a specific order, and we line up the actions to match the order. Since the
order is important here, we should make it explicit using a sequence:
```cpp
using ::testing::InSequence;
using ::testing::Return;
...
{
InSequence s;
for (int i = 1; i <= n; i++) {
EXPECT_CALL(turtle, GetX())
.WillOnce(Return(10*i))
.RetiresOnSaturation();
}
}
```
By the way, the other situation where an expectation may *not* be sticky is when
it's in a sequence - as soon as another expectation that comes after it in the
sequence has been used, it automatically retires (and will never be used to
match any call).
#### Uninteresting Calls
A mock object may have many methods, and not all of them are that interesting.
For example, in some tests we may not care about how many times `GetX()` and
`GetY()` get called.
In gMock, if you are not interested in a method, just don't say anything about
it. If a call to this method occurs, you'll see a warning in the test output,
but it won't be a failure. This is called "naggy" behavior; to change, see
[The Nice, the Strict, and the Naggy](cook_book.md#NiceStrictNaggy).

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@ -1,396 +0,0 @@
## Legacy gMock FAQ {#GMockFaq}
<!-- GOOGLETEST_CM0021 DO NOT DELETE -->
### When I call a method on my mock object, the method for the real object is invoked instead. What's the problem?
In order for a method to be mocked, it must be *virtual*, unless you use the
[high-perf dependency injection technique](#MockingNonVirtualMethods).
### Can I mock a variadic function?
You cannot mock a variadic function (i.e. a function taking ellipsis (`...`)
arguments) directly in gMock.
The problem is that in general, there is *no way* for a mock object to know how
many arguments are passed to the variadic method, and what the arguments' types
are. Only the *author of the base class* knows the protocol, and we cannot look
into his or her head.
Therefore, to mock such a function, the *user* must teach the mock object how to
figure out the number of arguments and their types. One way to do it is to
provide overloaded versions of the function.
Ellipsis arguments are inherited from C and not really a C++ feature. They are
unsafe to use and don't work with arguments that have constructors or
destructors. Therefore we recommend to avoid them in C++ as much as possible.
### MSVC gives me warning C4301 or C4373 when I define a mock method with a const parameter. Why?
If you compile this using Microsoft Visual C++ 2005 SP1:
```cpp
class Foo {
...
virtual void Bar(const int i) = 0;
};
class MockFoo : public Foo {
...
MOCK_METHOD(void, Bar, (const int i), (override));
};
```
You may get the following warning:
```shell
warning C4301: 'MockFoo::Bar': overriding virtual function only differs from 'Foo::Bar' by const/volatile qualifier
```
This is a MSVC bug. The same code compiles fine with gcc, for example. If you
use Visual C++ 2008 SP1, you would get the warning:
```shell
warning C4373: 'MockFoo::Bar': virtual function overrides 'Foo::Bar', previous versions of the compiler did not override when parameters only differed by const/volatile qualifiers
```
In C++, if you *declare* a function with a `const` parameter, the `const`
modifier is ignored. Therefore, the `Foo` base class above is equivalent to:
```cpp
class Foo {
...
virtual void Bar(int i) = 0; // int or const int? Makes no difference.
};
```
In fact, you can *declare* `Bar()` with an `int` parameter, and define it with a
`const int` parameter. The compiler will still match them up.
Since making a parameter `const` is meaningless in the method declaration, we
recommend to remove it in both `Foo` and `MockFoo`. That should workaround the
VC bug.
Note that we are talking about the *top-level* `const` modifier here. If the
function parameter is passed by pointer or reference, declaring the pointee or
referee as `const` is still meaningful. For example, the following two
declarations are *not* equivalent:
```cpp
void Bar(int* p); // Neither p nor *p is const.
void Bar(const int* p); // p is not const, but *p is.
```
<!-- GOOGLETEST_CM0030 DO NOT DELETE -->
### I can't figure out why gMock thinks my expectations are not satisfied. What should I do?
You might want to run your test with `--gmock_verbose=info`. This flag lets
gMock print a trace of every mock function call it receives. By studying the
trace, you'll gain insights on why the expectations you set are not met.
If you see the message "The mock function has no default action set, and its
return type has no default value set.", then try
[adding a default action](for_dummies.md#DefaultValue). Due to a known issue,
unexpected calls on mocks without default actions don't print out a detailed
comparison between the actual arguments and the expected arguments.
### My program crashed and `ScopedMockLog` spit out tons of messages. Is it a gMock bug?
gMock and `ScopedMockLog` are likely doing the right thing here.
When a test crashes, the failure signal handler will try to log a lot of
information (the stack trace, and the address map, for example). The messages
are compounded if you have many threads with depth stacks. When `ScopedMockLog`
intercepts these messages and finds that they don't match any expectations, it
prints an error for each of them.
You can learn to ignore the errors, or you can rewrite your expectations to make
your test more robust, for example, by adding something like:
```cpp
using ::testing::AnyNumber;
using ::testing::Not;
...
// Ignores any log not done by us.
EXPECT_CALL(log, Log(_, Not(EndsWith("/my_file.cc")), _))
.Times(AnyNumber());
```
### How can I assert that a function is NEVER called?
```cpp
using ::testing::_;
...
EXPECT_CALL(foo, Bar(_))
.Times(0);
```
<!-- GOOGLETEST_CM0031 DO NOT DELETE -->
### I have a failed test where gMock tells me TWICE that a particular expectation is not satisfied. Isn't this redundant?
When gMock detects a failure, it prints relevant information (the mock function
arguments, the state of relevant expectations, and etc) to help the user debug.
If another failure is detected, gMock will do the same, including printing the
state of relevant expectations.
Sometimes an expectation's state didn't change between two failures, and you'll
see the same description of the state twice. They are however *not* redundant,
as they refer to *different points in time*. The fact they are the same *is*
interesting information.
### I get a heapcheck failure when using a mock object, but using a real object is fine. What can be wrong?
Does the class (hopefully a pure interface) you are mocking have a virtual
destructor?
Whenever you derive from a base class, make sure its destructor is virtual.
Otherwise Bad Things will happen. Consider the following code:
```cpp
class Base {
public:
// Not virtual, but should be.
~Base() { ... }
...
};
class Derived : public Base {
public:
...
private:
std::string value_;
};
...
Base* p = new Derived;
...
delete p; // Surprise! ~Base() will be called, but ~Derived() will not
// - value_ is leaked.
```
By changing `~Base()` to virtual, `~Derived()` will be correctly called when
`delete p` is executed, and the heap checker will be happy.
### The "newer expectations override older ones" rule makes writing expectations awkward. Why does gMock do that?
When people complain about this, often they are referring to code like:
```cpp
using ::testing::Return;
...
// foo.Bar() should be called twice, return 1 the first time, and return
// 2 the second time. However, I have to write the expectations in the
// reverse order. This sucks big time!!!
EXPECT_CALL(foo, Bar())
.WillOnce(Return(2))
.RetiresOnSaturation();
EXPECT_CALL(foo, Bar())
.WillOnce(Return(1))
.RetiresOnSaturation();
```
The problem, is that they didn't pick the **best** way to express the test's
intent.
By default, expectations don't have to be matched in *any* particular order. If
you want them to match in a certain order, you need to be explicit. This is
gMock's (and jMock's) fundamental philosophy: it's easy to accidentally
over-specify your tests, and we want to make it harder to do so.
There are two better ways to write the test spec. You could either put the
expectations in sequence:
```cpp
using ::testing::Return;
...
// foo.Bar() should be called twice, return 1 the first time, and return
// 2 the second time. Using a sequence, we can write the expectations
// in their natural order.
{
InSequence s;
EXPECT_CALL(foo, Bar())
.WillOnce(Return(1))
.RetiresOnSaturation();
EXPECT_CALL(foo, Bar())
.WillOnce(Return(2))
.RetiresOnSaturation();
}
```
or you can put the sequence of actions in the same expectation:
```cpp
using ::testing::Return;
...
// foo.Bar() should be called twice, return 1 the first time, and return
// 2 the second time.
EXPECT_CALL(foo, Bar())
.WillOnce(Return(1))
.WillOnce(Return(2))
.RetiresOnSaturation();
```
Back to the original questions: why does gMock search the expectations (and
`ON_CALL`s) from back to front? Because this allows a user to set up a mock's
behavior for the common case early (e.g. in the mock's constructor or the test
fixture's set-up phase) and customize it with more specific rules later. If
gMock searches from front to back, this very useful pattern won't be possible.
### gMock prints a warning when a function without EXPECT_CALL is called, even if I have set its behavior using ON_CALL. Would it be reasonable not to show the warning in this case?
When choosing between being neat and being safe, we lean toward the latter. So
the answer is that we think it's better to show the warning.
Often people write `ON_CALL`s in the mock object's constructor or `SetUp()`, as
the default behavior rarely changes from test to test. Then in the test body
they set the expectations, which are often different for each test. Having an
`ON_CALL` in the set-up part of a test doesn't mean that the calls are expected.
If there's no `EXPECT_CALL` and the method is called, it's possibly an error. If
we quietly let the call go through without notifying the user, bugs may creep in
unnoticed.
If, however, you are sure that the calls are OK, you can write
```cpp
using ::testing::_;
...
EXPECT_CALL(foo, Bar(_))
.WillRepeatedly(...);
```
instead of
```cpp
using ::testing::_;
...
ON_CALL(foo, Bar(_))
.WillByDefault(...);
```
This tells gMock that you do expect the calls and no warning should be printed.
Also, you can control the verbosity by specifying `--gmock_verbose=error`. Other
values are `info` and `warning`. If you find the output too noisy when
debugging, just choose a less verbose level.
### How can I delete the mock function's argument in an action?
If your mock function takes a pointer argument and you want to delete that
argument, you can use testing::DeleteArg<N>() to delete the N'th (zero-indexed)
argument:
```cpp
using ::testing::_;
...
MOCK_METHOD(void, Bar, (X* x, const Y& y));
...
EXPECT_CALL(mock_foo_, Bar(_, _))
.WillOnce(testing::DeleteArg<0>()));
```
### How can I perform an arbitrary action on a mock function's argument?
If you find yourself needing to perform some action that's not supported by
gMock directly, remember that you can define your own actions using
[`MakeAction()`](#NewMonoActions) or
[`MakePolymorphicAction()`](#NewPolyActions), or you can write a stub function
and invoke it using [`Invoke()`](#FunctionsAsActions).
```cpp
using ::testing::_;
using ::testing::Invoke;
...
MOCK_METHOD(void, Bar, (X* p));
...
EXPECT_CALL(mock_foo_, Bar(_))
.WillOnce(Invoke(MyAction(...)));
```
### My code calls a static/global function. Can I mock it?
You can, but you need to make some changes.
In general, if you find yourself needing to mock a static function, it's a sign
that your modules are too tightly coupled (and less flexible, less reusable,
less testable, etc). You are probably better off defining a small interface and
call the function through that interface, which then can be easily mocked. It's
a bit of work initially, but usually pays for itself quickly.
This Google Testing Blog
[post](https://testing.googleblog.com/2008/06/defeat-static-cling.html) says it
excellently. Check it out.
### My mock object needs to do complex stuff. It's a lot of pain to specify the actions. gMock sucks!
I know it's not a question, but you get an answer for free any way. :-)
With gMock, you can create mocks in C++ easily. And people might be tempted to
use them everywhere. Sometimes they work great, and sometimes you may find them,
well, a pain to use. So, what's wrong in the latter case?
When you write a test without using mocks, you exercise the code and assert that
it returns the correct value or that the system is in an expected state. This is
sometimes called "state-based testing".
Mocks are great for what some call "interaction-based" testing: instead of
checking the system state at the very end, mock objects verify that they are
invoked the right way and report an error as soon as it arises, giving you a
handle on the precise context in which the error was triggered. This is often
more effective and economical to do than state-based testing.
If you are doing state-based testing and using a test double just to simulate
the real object, you are probably better off using a fake. Using a mock in this
case causes pain, as it's not a strong point for mocks to perform complex
actions. If you experience this and think that mocks suck, you are just not
using the right tool for your problem. Or, you might be trying to solve the
wrong problem. :-)
### I got a warning "Uninteresting function call encountered - default action taken.." Should I panic?
By all means, NO! It's just an FYI. :-)
What it means is that you have a mock function, you haven't set any expectations
on it (by gMock's rule this means that you are not interested in calls to this
function and therefore it can be called any number of times), and it is called.
That's OK - you didn't say it's not OK to call the function!
What if you actually meant to disallow this function to be called, but forgot to
write `EXPECT_CALL(foo, Bar()).Times(0)`? While one can argue that it's the
user's fault, gMock tries to be nice and prints you a note.
So, when you see the message and believe that there shouldn't be any
uninteresting calls, you should investigate what's going on. To make your life
easier, gMock dumps the stack trace when an uninteresting call is encountered.
From that you can figure out which mock function it is, and how it is called.
### I want to define a custom action. Should I use Invoke() or implement the ActionInterface interface?
Either way is fine - you want to choose the one that's more convenient for your
circumstance.
Usually, if your action is for a particular function type, defining it using
`Invoke()` should be easier; if your action can be used in functions of
different types (e.g. if you are defining `Return(*value*)`),
`MakePolymorphicAction()` is easiest. Sometimes you want precise control on what
types of functions the action can be used in, and implementing `ActionInterface`
is the way to go here. See the implementation of `Return()` in
`testing/base/public/gmock-actions.h` for an example.
### I use SetArgPointee() in WillOnce(), but gcc complains about "conflicting return type specified". What does it mean?
You got this error as gMock has no idea what value it should return when the
mock method is called. `SetArgPointee()` says what the side effect is, but
doesn't say what the return value should be. You need `DoAll()` to chain a
`SetArgPointee()` with a `Return()` that provides a value appropriate to the API
being mocked.
See this [recipe](cook_book.md#mocking-side-effects) for more details and an
example.
### I have a huge mock class, and Microsoft Visual C++ runs out of memory when compiling it. What can I do?
We've noticed that when the `/clr` compiler flag is used, Visual C++ uses 5~6
times as much memory when compiling a mock class. We suggest to avoid `/clr`
when compiling native C++ mocks.

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@ -1,187 +0,0 @@
<b>P</b>ump is <b>U</b>seful for <b>M</b>eta <b>P</b>rogramming.
# The Problem
Template and macro libraries often need to define many classes, functions, or
macros that vary only (or almost only) in the number of arguments they take.
It's a lot of repetitive, mechanical, and error-prone work.
Our experience is that it's tedious to write custom scripts, which tend to
reflect the structure of the generated code poorly and are often hard to read
and edit. For example, a small change needed in the generated code may require
some non-intuitive, non-trivial changes in the script. This is especially
painful when experimenting with the code.
This script may be useful for generating meta code, for example a series of
macros of FOO1, FOO2, etc. Nevertheless, please make it your last resort
technique by favouring C++ template metaprogramming or variadic macros.
# Our Solution
Pump (for Pump is Useful for Meta Programming, Pretty Useful for Meta
Programming, or Practical Utility for Meta Programming, whichever you prefer) is
a simple meta-programming tool for C++. The idea is that a programmer writes a
`foo.pump` file which contains C++ code plus meta code that manipulates the C++
code. The meta code can handle iterations over a range, nested iterations, local
meta variable definitions, simple arithmetic, and conditional expressions. You
can view it as a small Domain-Specific Language. The meta language is designed
to be non-intrusive (s.t. it won't confuse Emacs' C++ mode, for example) and
concise, making Pump code intuitive and easy to maintain.
## Highlights
* The implementation is in a single Python script and thus ultra portable: no
build or installation is needed and it works cross platforms.
* Pump tries to be smart with respect to
[Google's style guide](https://github.com/google/styleguide): it breaks long
lines (easy to have when they are generated) at acceptable places to fit
within 80 columns and indent the continuation lines correctly.
* The format is human-readable and more concise than XML.
* The format works relatively well with Emacs' C++ mode.
## Examples
The following Pump code (where meta keywords start with `$`, `[[` and `]]` are
meta brackets, and `$$` starts a meta comment that ends with the line):
```
$var n = 3 $$ Defines a meta variable n.
$range i 0..n $$ Declares the range of meta iterator i (inclusive).
$for i [[
$$ Meta loop.
// Foo$i does blah for $i-ary predicates.
$range j 1..i
template <size_t N $for j [[, typename A$j]]>
class Foo$i {
$if i == 0 [[
blah a;
]] $elif i <= 2 [[
blah b;
]] $else [[
blah c;
]]
};
]]
```
will be translated by the Pump compiler to:
```cpp
// Foo0 does blah for 0-ary predicates.
template <size_t N>
class Foo0 {
blah a;
};
// Foo1 does blah for 1-ary predicates.
template <size_t N, typename A1>
class Foo1 {
blah b;
};
// Foo2 does blah for 2-ary predicates.
template <size_t N, typename A1, typename A2>
class Foo2 {
blah b;
};
// Foo3 does blah for 3-ary predicates.
template <size_t N, typename A1, typename A2, typename A3>
class Foo3 {
blah c;
};
```
In another example,
```
$range i 1..n
Func($for i + [[a$i]]);
$$ The text between i and [[ is the separator between iterations.
```
will generate one of the following lines (without the comments), depending on
the value of `n`:
```cpp
Func(); // If n is 0.
Func(a1); // If n is 1.
Func(a1 + a2); // If n is 2.
Func(a1 + a2 + a3); // If n is 3.
// And so on...
```
## Constructs
We support the following meta programming constructs:
| `$var id = exp` | Defines a named constant value. `$id` is |
: : valid util the end of the current meta :
: : lexical block. :
| :------------------------------- | :--------------------------------------- |
| `$range id exp..exp` | Sets the range of an iteration variable, |
: : which can be reused in multiple loops :
: : later. :
| `$for id sep [[ code ]]` | Iteration. The range of `id` must have |
: : been defined earlier. `$id` is valid in :
: : `code`. :
| `$($)` | Generates a single `$` character. |
| `$id` | Value of the named constant or iteration |
: : variable. :
| `$(exp)` | Value of the expression. |
| `$if exp [[ code ]] else_branch` | Conditional. |
| `[[ code ]]` | Meta lexical block. |
| `cpp_code` | Raw C++ code. |
| `$$ comment` | Meta comment. |
**Note:** To give the user some freedom in formatting the Pump source code, Pump
ignores a new-line character if it's right after `$for foo` or next to `[[` or
`]]`. Without this rule you'll often be forced to write very long lines to get
the desired output. Therefore sometimes you may need to insert an extra new-line
in such places for a new-line to show up in your output.
## Grammar
```ebnf
code ::= atomic_code*
atomic_code ::= $var id = exp
| $var id = [[ code ]]
| $range id exp..exp
| $for id sep [[ code ]]
| $($)
| $id
| $(exp)
| $if exp [[ code ]] else_branch
| [[ code ]]
| cpp_code
sep ::= cpp_code | empty_string
else_branch ::= $else [[ code ]]
| $elif exp [[ code ]] else_branch
| empty_string
exp ::= simple_expression_in_Python_syntax
```
## Code
You can find the source code of Pump in [scripts/pump.py](../scripts/pump.py).
It is still very unpolished and lacks automated tests, although it has been
successfully used many times. If you find a chance to use it in your project,
please let us know what you think! We also welcome help on improving Pump.
## Real Examples
You can find real-world applications of Pump in
[Google Test](https://github.com/google/googletest/tree/master/googletest) and
[Google Mock](https://github.com/google/googletest/tree/master/googlemock). The
source file `foo.h.pump` generates `foo.h`.
## Tips
* If a meta variable is followed by a letter or digit, you can separate them
using `[[]]`, which inserts an empty string. For example `Foo$j[[]]Helper`
generate `Foo1Helper` when `j` is 1.
* To avoid extra-long Pump source lines, you can break a line anywhere you
want by inserting `[[]]` followed by a new line. Since any new-line
character next to `[[` or `]]` is ignored, the generated code won't contain
this new line.